I think there were at least three significant changes in the last 11 years of the 216/235/261 distributors:
1. Rotor and cap changed (in 1953?)
2. Cam gear changed (in 1953 or 1954?)
3.
Primary Terminal changed (in 1953 - see link below)
It looks like you are referring to the later style Primary Terminal (you might be able to use the earlier style terminal assembly but the later style has "stops" in the Bakelite pieces and seems to be a better design and it matches the hole through the distributor body (you need to obtain or make
a special tool to tighten the round "nut" used on these 1953 and later distributors.
Maybe someone knows a vendor that sells the 1953-1963 distributor's Primary Terminal but I agree with Jerry - look for a 1954 or newer used or rebuilt distributor (try an ad in the Swap Meet - maybe someone will send you the terminal assembly). I think that all 1954 and later distributors had a cam gear that was safe with the later cams.
